Pair of substrates spaced from each other by spacers having a pre-determined pattern and method of making thereof

ABSTRACT

The invention pertains to a method of obtaining a pair of substrates spaced from each other by spacers comprising: a) providing a first substrate overlaid with a first layer with a patterned hydrophobic second layer or a patterned hydrophilic second layer that can take on an electrostatic charge; and b) optionally treating the parts of the first layer that are not covered with the hydrophobic or hydrophilic second layer to form a patterned hydrophilic third layer that can take on an electrostatic charge with a sign that is opposite to the sign of the electrostatic charge that can be taken on by the hydrophilic second layer, if the second layer is a hydrophilic layer; c) providing at least one of the first, second, and third layer with an electrostatic charge; d) contacting the electrostatically charged patterned first substrate with a dispersion of polymeric particles (spacers), which are functionalized so that the polymeric particles at their surface can take on an electrostatic charge with a sign opposite to the sign of the electrostatic charge of the at least one of the first, second, and third layer, to electrostatically bond the polymeric particles to the layer provided with an electrostatic charge having a sign that is opposite to the sign of the electrostatic charge of the polymeric particles; e) optionally removing the functionalized polymeric particles from parts to which the functionalized polymeric particles are not electrostatically bonded, and/or the hydrophobic or hydrophilic second layer, if the polymeric particles are not electrostatically bonded thereto; and f) thereafter connecting the first substrate to a second substrate to give the pair of substrates.

The invention pertains to a method of obtaining a pair of substratesspaced from each other by spacers, to said pair of substrates spacedfrom each other by spacers, and to a device and an LCD displaycomprising the pair of substrates spaced from each other by spacers.

In a liquid crystal cell of a device such as a liquid crystalelectro-optical device, the spacing between the substrates in the cellis generally maintained constant by sparsely distributing silicon oxidespheres about several micrometers in diameter as spacers between thesubstrates. The spacers are thus held between the substrates to maintainthe distance between the substrates at a constant value. The distance isdetermined by the diameter of the spacers. The spacers assure theminimum spacing between the substrates; i.e., they prevent a decrease indistance between the substrates from occurring. Spacers placed accordingto a regular geometrical pattern are more effective to control the cellgap homogeneously, particularly for plastic substrates.

When such spacers are used for maintaining the spacing between thesubstrates constant, a liquid crystal display having a large imagedisplay area using a liquid crystal, particularly ferro-electric liquidcrystal, is unfeasible because the display experiences disturbances.This problem occurs in the liquid crystal displays using not onlyferro-electric liquid crystals but also any kind of liquid crystalmaterials. To avoid this problem, in addition to the spacers, adhesivematerials (scattered in a liquid crystal cell) based on an organic resinfor fixing the spacing between the substrates are used. These types oforganic resin adhesives are provided as spheres larger than the spacingbetween the substrates so that they may deform and tightly adhere onesubstrate to the other upon applying pressure thereto.

In U.S. Pat. No. 5,739,882 a fabrication process has been disclosed formaking such liquid crystal electro-optical devices. According to thisfabrication process resin columns are prepared by bringing uncured resinonto desired positions of the substrate and curing the resin material sothat polymerized spacers are formed. This process, however, has somedrawbacks. Firstly, before the column-like spacers are formed at thedesired positions, the pair of substrates must be kept at the desiredpredetermined distance by using “temporary” spacers that are scatteredrandomly between the pair of substrates and which cannot be removedafter the permanently cured resin spacers have been formed. Then the twosubstrates are fixed by adhering them together using a two-liquid epoxyresin adhesive as the sealing material. The two-liquid epoxy resinadhesive is applied to the periphery of one of the substrates byscreen-printing, and the two substrates are adhered to fix. The platefor screen-printing is oriented with the substrate in such a manner thateach of the warps and the wefts may be superposed to the positionscorresponding to the scanning electrodes and the signal electrodes,respectively. Secondly, the prior art method at least needs extraproduction steps, i.e. scattering the temporary spacers between thesubstrates, performing a curing step of the resin to obtain column-likespacers. Such complicated method of manufacture makes the device moreexpensive. Furthermore, this method leads to unpolymerized contaminants,which compromise the electro-optic performance of the device.

It is therefore an object of the present invention to obtain a method ofdistancing the pair of substrate in a simple manner, without the need tomake use of temporary spacers and simplifying the method of productionconsiderably.

To this end a method was found wherein a pair of substrates is obtainedby a procedure wherein a pair of substrates is spaced from each other byspacers comprising:

-   -   a) providing a first substrate overlaid with a first layer with        a patterned hydrophobic second layer or a patterned hydrophilic        second layer that can take on an electrostatic charge; and    -   b) optionally treating the parts of the first layer that are not        covered with the hydrophobic or hydrophilic second layer to form        a patterned hydrophilic third layer that can take on an        electrostatic charge with a sign that is opposite to the sign of        the electrostatic charge that can be taken on by the hydrophilic        second layer, if the second layer is a hydrophilic layer;    -   c) providing at least one of the first, second, and third layer        with an electrostatic charge;    -   d) contacting the electrostatically charged patterned first        substrate with a dispersion of polymeric particles (spacers),        which are functionalized so that the polymeric particles at        their surface can take on an electrostatic charge with a sign        opposite to the sign of the electrostatic charge of the at least        one of the first, second, and third layer, to electrostatically        bond the polymeric particles to the layer provided with an        electrostatic charge having a sign that is opposite to the sign        of the electrostatic charge of the polymeric particles;    -   e) optionally removing the functionalized polymeric particles        from parts to which the functionalized polymeric particles are        not electrostatically bonded, and/or the hydrophobic or        hydrophilic second layer, if the polymeric particles are not        electrostatically bonded thereto; and    -   f) thereafter connecting the first substrate to a second        substrate to give the pair of substrates.

In step a) the first layer can be patterned, leaving insulating areasexposed. The first layer can be of any material, but usually it is analignment layer, such as a polyimide, or a conductive or semi-conductivelayer, such as an ITO layer, which can chemically be patterned. It isalso possible that the first layer is a conductive or semi-conductivelayer overlaid with an alignment layer. The first layer can be part of aflexible polymer-based substrate or an inflexible substrate such as aglass substrate. The first layer can also be an integral part of thesubstrate, for instance the top layer of a metallic substrate. Thesecond layer is made of a hydrophobic or hydrophilic compound and may,for instance, be a patterned self-assembled monolayer (SAM) of protectedhydrophobic molecules, such as octadecyltrichlorosilane (OTS) and thelike, which can be applied in a conventional manner as known by theartisan, such as by micro-contact printing with a silicon rubber stamp.Hydrophylic layers can be made of3-(2-aminoethylamino)propyltrimethoxysilane,3-aminopropyl-3-methoxysilane, and the like, as is known to the skilledperson. When the first layer is a conductive or semi-conductive layer,this layer can take on an electrostatic charge by chemical treatment,for instance by treating an ITO layer with hydrogen chloride, or byapplying an electric voltage. Hydrophilic second and third layers can becharged by applying a suitable pH, after which acidic or basic groupsare converted to anionic and cationic groups, respectively.

The polymeric spacers are end-functionalized with a group that can beelectrostatically charged, such as an acid group like carboxylic acid,sulfonic acid, phosphonic acid, and the like, which at a suitable pH areconverted to negatively charged carboxylate, sulfonate, and phosphonategroups, respectively. The end group may also be a basic group such as anamine, preferably primary and tertiary amine, which groups can take on apositive electrostatic charge at the suitable pH. The spacers may haveany form, among which column-like, ellipsoidal, cylindrical, andspherical. Spherical and spherical-like particles are preferred, morepreferably having diameter of about 1 μm to about 10 μm, since they areeasily available and can advantageously be attached to pre-determinedsites. Substrates making use of these end-functionalized particles arenovel and are also an embodiment of the present invention. In a suitablemethod, after patterning, the substrates are dipped in a watersuspension or dispersion of such particles. In a suitable embodiment thepolymeric spacers selectively absorb to the non-protected (non-covered)parts of the first layer surface and excess of spacer can easily berinsed off. The pH of the solution may be adjusted to optimize theprocess in one or more of its characteristics, among which rate andinteraction strength. An alternative of this process is to deposit anintermediate SAM or a linear or dendritic polyelectrolyte layer onto theuncovered areas before contacting it with the spacer. It is stressedthat this alternative includes the combination of differentsoft-lithographic and deposition steps. After these processes orientingmeans for orienting (aligning) the liquid crystal molecules along onedirection may be provided on the inner side of at least one of the pairof substrates, so that the liquid crystals are oriented optionally afterrubbing the layer before alignment.

It is preferred to position clusters of spacers such that they do notinterfere with the optical performance of the device, i.e. preferablynot on the surface of a pixel, but only at the edges or corners thereof.

In a related aspect, the invention relates to a pair of substratesspaced from each other by polymeric particles (spacers) wherein thepolymeric particles are positioned between the pair of substrates in apre-determined pattern and are functionalized so that the polymericparticles at their surface have groups that can take on an electrostaticcharge. In particular, the particles can take on a charge with a signthat is opposite to the sign of the electrostatic charge that can betaken on by at least one of the first, second, or third layer to whichit is in contact.

The principle of the present method is illustrated in FIGS. 1-4.

FIG. 1 shows a substrate with a charged first layer, which is patternedby a hydrophobic second layer, and functionalized spacers.

FIG. 2 shows an alternative of FIG. 1 with a hydrophilic second and athird layer.

FIG. 3 shows an alternative of FIG. 2 wherein the hydrophilic thirdlayer is a polyelectrolyte or a dendrimer.

FIG. 4 shows a substrate, with a first layer and a hydrophilic second orthird layer and spacers bonded thereto.

Referring to FIG. 1, a part of a liquid crystal electro-optical deviceis shown utilizing spherical functionalized spacers 1, comprising alight-transmitting substrate 2. Not shown in FIGS. 1-4 are the secondsubstrate that is placed onto the first substrate and spaced to aspecified distance from the first substrate by the spacers, and optionalelectrodes, orientation films, liquid crystal material, and sealingmaterial. The spacers have, for instance, an electrostatic negativecharge and are bonded to the first layer 3, which in this particularcase is an ITO layer that is chemically modified by hydrogen chloride togive a positive electrostatic charge. The spacers have no interactionwith the hydrophobic second layer 4 (for instance an OTS layer) that ispatterned onto the first layer 3 and these areas are therefore free formpolymeric particles 1.

In FIG. 2 the situation is depicted wherein the second layer 4 is not ahydrophobic layer (such as OTS), but a negatively charged hydrophiliclayer. The areas of first layer 3 that are not covered by thehydrophilic second layer 4 are then provided with a hydrophilic thirdlayer 5 having a positive electrostatic charge, which is opposite to thecharge of the hydrophilic second layer. The negatively charges spacersadhere to the positively charged third layer 5, and not to thenegatively charged second layer 4. After bonding of the spacers 1, thesecond layer 4 may optionally be removed, after which a configuration isobtained that is depicted in FIG. 4, wherein number 6 then refers tohydrophilic third layer 5.

In FIG. 3 a special embodiment of FIG. 2 is shown, wherein the thirdlayer 5 is a high-molecular polyelectrolyte or a dendrimer to which thespacers bond.

FIG. 4 shows the situation wherein the hydrophobic or hydrophilic secondlayer 4 has been removed (from the embodiments as presented in FIGS. 2and 3) and wherein number 6 refers to third layer 5 (which also may beof the high-molecular polyelectrolyte or dendrimer type), which iselectrostatically bonded to the functionalized polymeric particles.

FIG. 4 also represents an embodiment wherein the second layer 4, havinggroups that are electrostatically charged with the sign opposite to thesign of the electrostatically charged polymeric particles 1, ispatterned onto the first layer, which is not charged or iselectrostatically charged with the same sign as that of theelectrostatically charged polymeric particles 1, after which thefunctionalized polymeric particles I are bonded to second layer 4. Forinstance, this embodiment is obtained when layer 3 is an alignment layerthat is directly provided onto the substrate. In this embodiment secondlayer 4 (indicated by number 6 in FIG. 4) may also be of thehigh-molecular polyelectrolyte or dendrimer type.

The above methods provide devices that are also an object of theinvention. Thus the invention also pertains to a device comprising twosubstrates spaced from each other by polymeric particles (spacers) 1, atleast the first substrate 2 being overlaid with a first layer 3 andpatterned by a hydrophobic or hydrophilic second layer 4, and optionallyby a hydrophilic third layer 5 that has an electrostatic charge with asign that is opposite to the sign of the electrostatic charge of thehydrophilic second layer, if the second layer is a hydrophilic layer;and wherein at least one of the first, second, and third layer has anelectrostatic charge, characterized in that the polymeric particles arepositioned between the pair of substrates in a pre-determined patternand are functionalized so that the polymeric particles at their surfacehave an electrostatic charge with a sign that is opposite to the sign ofthe electrostatic charge of at least one of the first, second, or thirdlayer to which the polymeric particles are electrostatically bonded.

Preferably, the spacers have a spherical or spherical-like shape aspreviously explained.

The invention is also particularly useful for application in LCDdisplays. LCD displays are well known in the art, see for example“Liquid Crystal Devices: Physics and Applications (Artech HouseOptoelectronics Library) Vladimir G. Chigrinov, pp. 215-2, Artech House;ISBN: 0890068984; (April 1999).

Such LCD displays may comprise a pair of substrates according to theinvention, preferably a pair of substrates spaced from each other bypolymeric particles (spacers), wherein the polymeric particles arepositioned between the pair of substrates in a pre-determined patternand are functionalized so that the polymeric particles at their surfacehave groups that can take on an electrostatic charge with a sign that isopposite to the sign of the electrostatic charge that can be taken on byat least one of the first, second, or third layer to which it is incontact.

The polymeric particles may be electrostatically bonded through theirfunctional groups to a charged layer it is also possible that thefunctionalized particles, dispersed in a medium wherein the functionalgroups can be ionized, are electrostatically bonded to a layer that ischarged by applying a voltage. For instance, a metal layer can becharged positively by applying a voltage, after which a dispersion ofcarboxylate-functional polymeric particles can electrostatically bond tosaid layer. After having the particles patterned in this manner, thevoltage can be removed after which the layer is not longer charged andthe charged carboxylate groups of the functionalized particles resumetheir uncharged carboxylic acid form. In such devices the particles arepositioned in a pre-determined pattern, but may not longer beelectrostatically bonded in the end product.

The liquid crystal material used in the present embodiment may be anysuitable liquid crystal material such as those disclosed in: LowMolecular Weight Liquid Crystals I, Volume 2A, Handbook of LiquidCrystals by George W. Gray (Editor), John W. Goodby (Editor), Hans W.Speiss (Editor), Edited by: Dietrich Demus, John Wiley & Sons; ISBN:3527292713; 1st edition (Mar. 10, 1998). Specific non-limitativeexamples are E7™ (ex Merck) and CS1014, a ferroelectric liquid crystalmanufactured by Chisso Corporation.

Indium tin oxide (ITO) is the electrode material by choice for use as afirst layer and is deposited on a glass substrate (10.times.10 cm inarea) by sputtering or vapor deposition to a thickness of from 50 to 200nm, specifically, 100 nm, and patterned by a conventionalphotolithography to obtain an electrode. Polyimide may be applied to thesurface of the resulting substrate by spin coating, and fired at 280° C.Polyimide suitable for use as the orientation film include RN-305 (aproduct of Nissan Chemical Industries, Ltd.) and LP-64 (a product ofToray Industries, Inc.). LP-64 is used specifically in the embodiment toform a polyimide film (15 nm in thickness). In general, the polyimidefilm is provided at a thickness of from 10 to 80 nm. The resultingsubstrate is then subjected to uniaxial orientation treatment by arubbing process, and a hydrophobic or hydrophilic layer is applied.Suitable layer are obtained with polystyrene sulfonate, polyacrylic acidsodium salt, octadecyltrichlorosilane, 3-aminopropyltrimethoxysilane,and 3-aminoethyl-2-aminopropyltrimethoxysilane. Micro-spherical polymerof latex particles functionalized with amine or carboxylate groups, suchas Polybead™ microspheres (ex Polyscience Inc., USA), functionalizedspheres (hydroxyl, carboxyl, sulfate, sulfonate, amino groups) fromMicroparticles GmbH, carboxy-modified microparticles from Seradyn; oramino- and carboxy-modified microparticles from Kisker-Biotech can beused.

Thus, as described in the foregoing, the present invention realizes aprocess for fabricating a liquid crystal electro-optical devicesimplified in process and shortened in process time.

THE INVENTION IS FURTHER ILLUSTRATED BY THE FOLLOWING NON-LIMITATIVEEXAMPLES

Materials and Chemicals

The following samples were all coated with an indiumtinoxide (ITO)conductive layer as the first layer.

Samples

substrates used are:

-   -   a) glass    -   b) synthetic resin foil from TEIJIN (code DT 120 B60)    -   c) synthetic resin foil OIKE-PET (code LR-TS)

The synthetic resin foils were clipped with a cutter using a microscopeslide as a pattern.

Microspheres (Polymeric Particles, Spacers)

Polybead™ microspheres (monodisperse polystyrene latex particles) withtwo different functional groups were used.

-   -   Amine-Functionalized    -   Carboxylate-functionalized.    -   The spheres were diluted in deionized water and measured in        drops.        Modifiers

To modify the ITO-surface the following polymers:

-   -   PSS (polystyrene sulfonate)    -   PM (polyacrylic acid, sodium salt)    -   as a hydrophilic second layer which can be provided with an        electrostatic charge and the molecules:    -   OTS (octadecyltrichlorosilane)    -   A 1100 (3-aminopropyltrimethoxysilane)    -   A 1120 (3-(2-aminoethylaminopropy)1trimethoxysilane)    -   were used for making a hydrophobic second layer.        Microspheres Solutions        Making the Solution

The microspheres were measured in drops (one drop weights approximately35 mg) and diluted with deionized water and optionally charged(pH-change) with using a strong acid like HCI (for the aminospheres) ora base like NaOH (for the carboxyspheres). Mostly uncharged solutionswere used.

Using the Solution

The microspheres solution for the dipping experiment was stirred using alab cooker and a magnetic stirrer. For the spin coating technique, ashook solution was dropped with a Pasteur pipette.

Sample Preparation

The sample substrates were cleaned with different cleaning technologiesbefore starting the experiment

-   -   Washing with ethanol and drying in air at RT    -   Washing with ethanol, wiping with a Kimberly-Clark cloth and        drying in the oven (333K), and the surface was activated by one        of the following procedures    -   UV-ozone    -   Plasma-oxygen

Electrostatic bonding of polymer particles to the at least one of thefirst the second or third layer.

Bonding of Microspheres Without Surface Modification

The samples were placed vertically in a plastic beaker with a solutionof microspheres. After the bath several cleaning techniques such as:

-   -   dipping in deionized water and/or ethanol,    -   spraying with deionized water and/or ethanol, and    -   blowing with pressed air, were performed.

The drying of the samples followed in air at room temperature (22° C.)or in the oven at 60 to 90° C.

Surface Modification (Dipping) and Bonding of Microspheres (Dipping)

Modifiers were used to increase the bonding-ability of the ITO. A normaldipping experiment, followed by a rinsing and/or cleaning step(water-ethanol) and drying in the oven at 60° C. The bonding part wasthe same as described above.

Surface Modification (Stamping) and Bonding of Microspheres (Dipping)

In the experiment a PDMS stamp was employed. (Reference: Xia, Y. N. andG. M. Whitesides (1998). “Soft lithography.” Annual Review of MaterialsScience 28: 153-184). The ink (modifier) was applied onto the stamp witha Pasteur pipette and the solution was spread by spin coating. To drythe stamp completely and to avoid a dirty pattern it was blown withpressed air for a few seconds. Then the stamp was turned and pressedwith the fingers onto the sample and removed after 5 seconds by using apair of tweezers. The bonding is described above.

Surface Modification (Stamping) and Bonding of Microspheres (SpinCoating)

The stamping part was the same as above. For the bonding, part of thestamped sample was mounted onto the chuck of the spin coater and themicrospheres solution was dropped with a Pasteur pipette. To give thespheres the possibility to bond to the surface, a waiting time(sedimentation time) was introduced. Spin coating at slow speed (1000rpm) was then used for removing the solution. The sample was completelydried by placing it in the oven at 60° C. for 10-15 minutes.

Results

Surface modifications were obtained by using PSS, PAA, A1000, and A1120followed by dipping the samples in a solution of microspheres, having aconcentration of 0.01 to 5 wt. % and a pH between 5 and 10. By addingNaOH the carboxylated spheres were charged and by adding HCI the ITOlayer was charged. Using a glass-ITO substrate andcarboxylate-functionalized microspheres in concentration (0.01 to 5 wt.%) a dip time of 5 min was sufficient to show a good coverage.

The non-adhering modifier molecules were removed to prevent acontamination of the microsphere solution during the bondingexperiments. Dipping in deionized water for a few seconds for severaliterations appears a good treatment. Other techniques like rinsing ordipping in flowing water can also be carried out. Non-bondedmicrospheres could be removed by dipping, rinsing and spraying, or byblowing with pressed air. After surface modification the samples weredried at 60° C.

1. A method of obtaining a pair of substrates spaced from each other byspacers comprising: a) providing a first substrate overlaid with a firstlayer with a patterned hydrophobic second layer or a patternedhydrophilic second layer that can take on an electrostatic charge; andb) optionally treating the parts of the first layer that are not coveredwith the hydrophobic or hydrophilic second layer to form a patternedhydrophilic third layer that can take on an electrostatic charge with asign that is opposite to the sign of the electrostatic charge that canbe taken on by the hydrophilic second layer, if the second layer is ahydrophilic layer; c) providing at least one of the first, second, andthird layer with an electrostatic charge; d) contacting theelectrostatically charged patterned first substrate with a dispersion ofpolymeric particles (spacers), which are functionalized so that thepolymeric particles at their surface can take on an electrostatic chargewith a sign opposite to the sign of the electrostatic charge of the atleast one of the first, second, and third layer, to electrostaticallybond the polymeric particles to the layer provided with an electrostaticcharge having a sign that is opposite to the sign of the electrostaticcharge of the polymeric particles; e) optionally removing thefunctionalized polymeric particles from parts to which thefunctionalized polymeric particles are not electrostatically bonded,and/or the hydrophobic or hydrophilic second layer, if the polymericparticles are not electrostatically bonded thereto; and f) thereafterconnecting the first substrate to a second substrate to give the pair ofsubstrates.
 2. The method according to claim 1 wherein the first layeris a conductive or semi-conductive layer.
 3. The method according toclaim 1 wherein the first layer is an alignment layer.
 4. The methodaccording to claim 2 wherein the conductive or semi-conductive layer isoverlaid with an alignment layer.
 5. The method according to claim 1wherein spherically shaped functionalized polymeric particles are used.6. The method according to claim 5 wherein polymeric particles are usedhaving a diameter of about 1 μm to about 10 μm.
 7. The method accordingto claim 1 wherein the polymeric particles are functionalized with acidgroups or basic groups.
 8. The method according to claim 1 wherein thepolymeric particles are functionalized with carboxylic acid or sulfonicacid groups or with amine groups.
 9. A device comprising two substratesspaced from each other by polymeric particles (spacers), at least thefirst substrate being overlaid with a first layer and patterned by ahydrophobic or hydrophilic second layer, and optionally by a hydrophilicthird layer that has an electrostatic charge with a sign that isopposite to the sign of the electrostatic charge of the hydrophilicsecond layer, if the second layer is a hydrophilic layer; and wherein atleast one of the first, second, and third layer has an electrostaticcharge, characterized in that the polymeric particles are positionedbetween the pair of substrates in a pre-determined pattern and arefunctionalized so that the polymeric particles at their surface have anelectrostatic charge with a sign that is opposite to the sign of theelectrostatic charge of at least one of the first, second, or thirdlayer to which the polymeric particles are electrostatically bonded. 10.A pair of substrates spaced from each other by polymeric particles(spacers) wherein the polymeric particles are positioned between thepair of substrates in a pre-determined pattern and are functionalized sothat the polymeric particles at their surface have groups that can takeon an electrostatic charge.
 11. An LCD display comprising the pair ofsubstrates of claim 10 wherein at least one of the substrates mayoptionally be provided with at least one layer selected from anelectrode layer and an alignment layer.